Question

A capillary tube, made of glass is dipped into mercury. Then:
A. mercury rises in the capillary tube
B. mercury descends in capillary tube
C. mercury rises and flows out of capillary tube
D. mercury neither rises nor descends in the capillary tube

Answer 1

A capillary tube is a glass tube with thick walls which are basically used in thermometers. It has a diameter and a length. It is used to control the flow of refrigerant. For a substance to ascend in the capillary tube, the intramolecular attraction of the molecules of the substance must be less than the intermolecular attraction between molecules of glass and substance.

Complete step by step answer:
We are given to find what happens to the level of mercury in the capillary glass tube when it is immersed in mercury.
A capillary tube is a glass tube with very less diameter and length which is used to control the flow of refrigerant. It is designed to change the liquid refrigerant with high pressure into a spray refrigerant with low pressure. This decrease in pressure is dependent on the length and diameter of the capillary tube.
So for a substance to be ascended in the capillary tube, its intramolecular attractions must be less than the intermolecular attractions between the substance and the glass molecules.
But in mercury, it is completely opposite. The intramolecular attractions between the mercury molecules are much higher. So the mercury molecules do not stick to the glass walls of the capillary tube and due to the effect of gravity, those molecules appear to fall down.
So when a capillary tube is immersed in mercury, mercury descends in the capillary tube forming a convex meniscus.

So, the correct answer is “Option B”.

Note:
Surface adhesion pulls up a liquid into the capillary tube to form a concave meniscus and the internal cohesion pulls the liquid down to form a convex meniscus. When the molecules of liquid, like water, are attracted to the container, then a concave meniscus will be formed. When the molecules of a liquid, like mercury, have a stronger attraction to each other than to the glass tube, then a convex meniscus will be formed.